Our customer met an issue, their product(speaker) using ADAU1451 had finished development stage and MP for a while, but their end customer returned the failures set to them (2 sets in this Feb, 3 sets in May of end, total 5 failures sets) from end user.
RD checked the root cause, found due to ADAU1451 DVDD pin can't get the 1.2V supply voltage from the transistor, so the whole set can't work. The five sets all have the same problem.
RD found the external PNP transistor (ST STD2805, all circuit followed the ADAU1452 EVB's reference circuit) near by ADAU1451 was no working, and the resistance value between BC junction have about 600 ohm.
RD try to short the Emitter and Collector pin of transistor directly, then the speaker can work normally; And RD removed the short circuit between the Emitter and Collector pin, the speaker can't work ,so they think the STD2805 was the root cause.
Our customer sent the transistor (STD2805) to ST to do FA analysis, but according to the FA result, the failures part is OK.
The FA samples returned to our customer, RD re-mounted the transistor into the speaker PCBA board, the speaker can work again.
Our customer want to know :
1. The internal 1.2V reference voltage how to be generated? Is by IOVDD 3.3V or others?
Is it the possible that the internal reference voltage cause the issue happened?
2. About the transistor, the part number follow ADAU1452 EVB, and have the issue happen.
What is the condition let the PNP transistor working? Power on sequence or others?
Above the problems, please kindly to help us advised it.
Thank you very much!!